chore: revert ratelimit per-rout config

[zhaohuabing]

Revert #5072

Some existing users may choose to keep using an old version of envoy while upgrading to new version of Envoy Gateway. To maintain compatibility, we're reverting this change so that rate limit configuration continues to work with older Envoy versions.

We can revisit this in a few versions, once we're confident that older Envoy versions are no longer in use.

[codecov]

Codecov Report

Attention: Patch coverage is 90.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 65.21%. Comparing base (096cb8d) to head (858f0d5).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/xds/translator/ratelimit.go	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5749      +/-   ##
==========================================
+ Coverage   65.19%   65.21%   +0.01%     
==========================================
  Files         214      214              
  Lines       34321    34450     +129     
==========================================
+ Hits        22377    22467      +90     
- Misses      10591    10623      +32     
- Partials     1353     1360       +7     

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[arkodg]

thanks @zhaohuabing